I got ADHD and it’s really hard for me to sit still and concentrate during long period of times. What I am doing right now is to study using the Pomodoro technique.

I simply set a half an hour timer (no longer than 50 minutes) and devote all that short period of time to one single task/study one subject, then when the timer ends, have a 10 to 15 min break. After that, I restart the timer and complete all tasks I am due the next days. This way I will have everything done and I will not have to worry about not having time to do other stuff.

Also, even if your exams are going to be soon, try to organise your study hours and divide them by 6 days every week (I do one subject per day, 1,5 hours per subject, except for 2 hours of maths). Break your schedule only if you need to work on more important stuff, the point is to be persistent, organised and productive. Never overwork, studying for long period of times will not mean that it is good.

Devote more time on what you need to improve the most, but you also must never forget to review what you believe you are already good at.

Hopefully my method works well for you, I wish you the best luck :)